This study was designed to examine if there is a difference in the cough reflex between younger and older persons. A difference might explain the greater susceptibility of older persons to respiratory tract infections and pneumonia.
The study was the first granted approval by the Food and Drug Administration under an Investigational New Drug (IND) protocol for human capsaicin inhalation investigation. Two groups of normal subjects were recruited. All had normal spirometry, were current non-smokers ≥ 10 years, had no prior/current respiratory disease/complaints and no history of allergy or asthma. Measurements of exhaled breath nitric oxide (ENO), impulse oscillometry (IOS), and spirometry were recorded. Capsaicin inhalation challenge testing was performed according to the method of Dicpinigaitis et al (Chest 123:685-8, 2003).
There were 27 participants with 17 younger (median age, 22; range, 18-27 yrs.) and 10 older persons (median age, 74; range, 67-77 yrs.) recruited. ENO was higher for older vs. younger subjects (37.8 and 22.2 ppb respectfully, p<0.006). There was a tendency for the capsaicin dose for cough initiation and C2 to be higher for older subjects, but there was no significant difference for C5. Mean values for log C2 and C5 were recorded, p values equaled 0.58 and 0.41 respectively. Serial IOS and FEV1 remained unchanged and showed good consistency. No adverse reactions were observed in any subject.
Capsaicin challenge using pharmaceutical grade capsaicin is safe for normal subjects of all ages. Serial monitoring with repeated IOS and spirometry showed good reproducibility. Elevated NO levels in the older age group suggested possible baseline airway inflammation and confirms our earlier published data. While there is some tendency for capsaicin cough initiation and C2 to be higher in older persons, the values among the 2 groups were similar for C5.
Cough reflex sensitivity and underlying inflammation may be important factors in determining why older people are more susceptible to respiratory tract infections and pneumonia.
D. Sams, None.